A Trusted Traveling Companion: The CEntrance HiFi M8 Portable Headphone Amp/DAC
CEntrance HiFi-M8 ($699)
With headphone makers delivering more and more headphones that are designed to be driven directly out of a smartphone or tablet, the need for a portable headphone amp is slowly dwindling. Attaching a headphone amp to your phone or portable player is always an act of self-encumbrance, and the loss of convenience simply may not be worth it...usually. But there are times when an audiophile simply must get their fix, and if it means you can't fit your phone in your pocket, so be it. Time to go big or go home to your big rig. That's when I reach for my CEntrance HiFi-M8 (pronounced "mate"), Astell&Kern AK120, and a couple of great cans like the Westone ES5 and Jerry Harvey JH13FP custom IEMs. I might throw a pair of Audeze LCD-3 or Sennheiser HD 800 as well, because this amp will drive anything.
The first thing you'll need to know about this amp is that it's available in eight different configurationstwo different input configurations, and four different front panel output configurations. Input configurations for the "HiFi-M8" is the ability to take digital outputs from iDevices with 30-pin outputs and a computer USB input; the "HiFi-M8 LX" swaps the iDevice port for a Toslink optical digital input, the computer USB input remains.
Four front panel output configurations are: XL4; RSA; CMB; and Pro. I use the XL4 version with a 4-pin balanced XLR out, and 1/4" and 3.5mm unbalanced jacks. On the front panel configurations with a 3.5mm jack (XL4, RSA) an optical digital output is also available on the 3.5mm jack allowing the M8 to be used as a USB-to-SPDIF converter. The RSA version uses the Kobiconn 163-191J-E 4-pin connector for balanced operation (part at Mouser, .pdf spec sheet).
The rear panel bristles with numerous controlswe'll go from left to right looking at the rear panel. Generally the switches give you "more" as you move them from left to right.
Output Impedance - Adjust output impedance of amp to (L to R) 10 Ohms, 2 Ohms, and 1Ohm. The lower the output impedance the more the amp has tight control of the driver in the headphones. The general wisdom is that the amp needs to have at least ten times lower impedance than the headphones for best performance. (For example, for a 30 Ohm headphone the output impedance of the amp should be 3 Ohms or less.) Generally speaking, I use the M8 at the lowest impedance and leave it there. But some listeners prefer the slightly more relaxed sound of a higher output impedance with higher impedance headphones. (Sennheiser HD 800 or HD 600, for example).
Output Level - This is similar to the gain switch many headphone amps have. The CEntrance specs state nominal output voltages as: -2dBV, -10dBV, and -22dBV (L to R on the switch). I assume "nominal" in this case is the average digital level of music. With 0dBF full level digital signal input and the volume control at max, I measure output voltages as: -5.4dBV, +7.7dBV, and +13.9dBV respectively. Bottom line: this amp has plenty of gain in the high settings, and has very low noise at the low settings; simply select the gain setting where your listening levels on the volume pot are between 12 and 3 o'clock and you're good to go.
Bass Tone Shaping - As you can see by the graph above, the bass tone control produces roughly +3dB and +6dB of gain in a relatively narrow peak centered at 80Hz. Personally, I think I would prefer a bass shelving filter that started at around 120Hz and went up to +3dB and +6dB and remained at that level down to 30Hz or so. I asked Michael Goodman about this, he said he preferred the shape in the current M8, and feels a shelving filter as I describe would have created a "muddy" bass. I felt the +3dB filter was useful occasionally, but the +6dB filter had too strong a tonal center and led to a significantly "one-note" character to the bass. It's worth noting here that the M8 is DC coupled throughout; the relatively small roll-off in the bass below 50Hz is likely caused by the circuit used to protect the unit from DC off-set (DC servo), and is not worrisome to me. I'll add that the shelving filter I described may have the potential to damage some headphones when high volumes are used. So, the CEntrance choice here may be the prudent one.
Treble Tone Shaping - In my experience, there are quite a few good headphones out there that lack response in the top octave (10kHz-20kHz). This filter provides a way to add some "air" to these headphones. For example, I very much like the Focal Spirit Professional headphone, but find them a little lacking in the last bit of resolution. It really doesn't "fix" the problem, but I do find I enjoy giving to top end a slight boost with the first treble boost. Likewise my Westone ES5 seems just a tad too rolled-off; using the treble boost in its highest setting seems to give me a sense of more air and clarity with these otherwise superb CIEMs.
Power and Source - This switch turn the M8 on and selects the desired input. Left to turn on and use the USB computer input; right to turn the power on and use the iDevice input, or the optical input on the LX model.
Battery Life - The battery life of the M8 is about 6 hours. That may not seem like a long time, but with all the no-compromise high-performance digital and analog circuitry in the unit a compromise must be drawn between battery life and the size of the amp needed to contain a large battery. I certainly wouldn't want the M8 to grow any bigger. Charging may take up to 6 hours and it's safe to leave the charger plugged as the unit will internally disconnect the charger when the battery is full, occasionally reconnecting to top off the battery.
USB DAC - CEntrance is fairly famous for its ongoing improvements to USB audio and the HiFi-M8 is capable of decoding USB audio up to 24/192 in asynchronous mode. Mac computer users will find the M8 USB plug and play; Windows users will have to download a USB driver here.
The HiFi-M8 can interface with USB On-The-Go compatible Android devices, but the issue is complex and universal compatibility is not guaranteed. CEntrance suggest using the USB Audio Player Pro, which includes its own proprietary USB OTG audio drivers.
Alright, enough of this product description stuff, flip the page and we'll talk about the listening experience.